System and method for suppressing silence in voice traffic over an asynchronous communication medium

ABSTRACT

A method and system for increasing the efficiency of providing bandwidth for voice traffic to a data provider via asynchronous communication mediums is provided. This is generally accomplished by not transmitting any data during the silence periods and playing out background noise (i.e., comfort noise) at the other end, to obtain significant bandwidth savings.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.09/783,405, filed Feb. 15, 2001, which is a continuation-in-part of U.S.patent application Ser. No. 09/427,792, filed Oct. 27, 1999, now U.S.Pat. No. 6,804,251, issued Oct. 12, 2004, both of which are hereinincorporated by reference in their entireties.

U.S. patent application Ser. No. 09/783,405 claims the benefit of U.S.Provisional Application No. 60/182,470, filed Feb. 15, 2000; U.S.Provisional Application No. 60/247,188, filed Nov. 9, 2000; U.S.Provisional Application No. 60/254,415, filed Dec. 8, 2000; U.S.Provisional Application No. 60/262,201, filed Jan. 17, 2001; and U.S.Provisional Application No. 60/262,203, filed Jan. 17, 2001, all ofwhich are herein incorporated by reference in their entireties.

U.S. patent application Ser. No. 09/783,405 is related to U.S. patentapplication Ser. No. 09/783,404, filed Feb. 15, 2001; U.S. patentapplication Ser. No. 09/785,020, filed Feb. 15, 2001; U.S. patentapplication Ser. No. 09/783,311, filed Feb. 15, 2001; and U.S. patentapplication Ser. No. 09/783,403, filed Feb. 15, 2001, all of which areherein incorporated by reference in their entireties.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention is generally related to increasing the efficiencyof providing bandwidth for voice traffic to a data provider viaasynchronous communication mediums.

2. Related Art

The importance to the modern economy of rapid data access and exchangecannot be overstated. This explains the exponentially increasingpopularity of the data access and exchange via cable networks (includingcoaxial cable or Hybrid fiber coaxial cable), the Internet, intranets,wireless networks, satellites and so forth (i.e., communicationmediums). Rapid data access and exchange is partly dependent upon howefficiently bandwidth is allocated to a data provider in order for thedata provider to transfer the requested data to a user via one of thecommunication mediums mentioned above.

One very desirable solution for rapid data access and exchange is viacable networks and cable modems. Cable modems provide asynchronouscommunications on cable networks. In general, a user connects a cablemodem to the TV outlet for his or her cable TV, and the cable TVoperator connects a cable modem termination system (“CMTS”) in theoperator's headend. The CMTS is a central device for connecting thecable network to a data network like the Internet. The CMTS is a centraldistribution point for a cable system. Data flows “downstream” from theCMTS to the cable modem (i.e., downstream communication). Alternatively,data flows “upstream” from the cable modem to the CMTS (i.e., upstreamcommunication).

A common cable modem standard today is the Data Over Cable ServiceInterface Specification (“DOCSIS”). DOCSIS defines technicalspecifications for both cable modems and CMTS. DOCSIS downstreamcommunication is quite restrictive in the way the control information isconveyed to the data provider (e.g., cable modem) via a DOCSIS CMTSscheduler. What is needed is to override the CMTS scheduler of DOCSISand provide a CMTS scheduler that increases the efficiency of providingbandwidth for voice traffic to a data provider via asynchronouscommunication mediums.

SUMMARY OF THE INVENTION

The present invention is generally related to increasing the efficiencyof providing bandwidth for voice traffic to a data provider viaasynchronous communication mediums. The present invention, by nottransmitting any data during the silence periods and playing outbackground noise (i.e., comfort noise) at the other end, obtainssignificant bandwidth savings.

The present invention includes a method for suppressing silence inbi-directional communications between a centralized node and a pluralityof local nodes in an asynchronous network environment, comprising thesteps of detecting a silent period in an upstream channel, the upstreamchannel transmitting data from a local node; and deactivatingunsolicited grant service in response to the detecting a silent period.

BRIEF DESCRIPTION OF THE FIGURES

The present invention will be described with reference to theaccompanying drawings, wherein:

FIG. 1 is a block diagram representing an example operating environmentof the present invention according to an embodiment of the presentinvention.

FIG. 2 illustrates a high level flowchart of unsolicited grant servicefor voice traffic according to an embodiment of the present invention.

FIG. 3 illustrates the format of an individual voice packet according toan embodiment of the present invention.

FIG. 4 is a flowchart illustrating the steps involved in reactivationmechanism of using priorities in contention minislots according to anembodiment of the present invention.

FIG. 5 illustrates the deactivation of unsolicited grant service (i.e.,deactivating a call when the call goes silent) according to anembodiment of the present invention.

FIG. 6 illustrates the activation of unsolicited grant service (i.e.,activating a call when the call becomes active) according to anembodiment of the present invention.

FIG. 7 is a formula showing how to compute the periodicity in seconds ofcontention minislots according to an embodiment of the presentinvention.

FIG. 8 illustrates the relationship between the periodicity of CMSs (T)and the probability of collision (Pc) for several numbers of silentusers (N) according to an embodiment of the present invention.

FIG. 9 illustrates an example computer used to implement the CMTS, theCMTS scheduler, the cable modem scheduler, the connection admissioncontrol and the contention resolution algorithm according to andembodiment of the present invention.

FIG. 10 is a flowchart that illustrates how the present inventiondetermines the number of contention minislots needed for voice priority.

DETAILED DESCRIPTION OF THE INVENTION

A. Overview of the Invention

The present invention, by not transmitting any data during the silenceperiods and playing out background noise (i.e., comfort noise) at theother end, obtains significant bandwidth savings. For illustrationpurposes, the present invention is described in terms of being utilizedwith a cable network. It should be understood that the present inventionis not limited to use with a cable network. In fact, the presentinvention may be used with any communication medium, including but notlimited to, the Internet, intranets, fiber optic networks, wirelessnetworks and satellites.

The present invention is described with reference to voice traffic orvoice data. But, data in the present invention includes any type ofinformation that is deterministic (i.e., a constant bit rate), such asvoice traffic. Also, it is important to note that the present inventionis not limited to voice traffic. In fact, the present invention can beused for any constant bit rate source with ON and OFF periods.

B. System Architecture Overview

FIG. 1 is a block diagram representing an example operating environmentof the present invention. It should be understood that the exampleoperating environment in FIG. 1 is shown for illustrative purposes onlyand does not limit the invention. Other implementations of the operatingenvironment described herein will be apparent to persons skilled in therelevant art(s) based on the teachings contained herein, and theinvention is directed to such other implementations. Referring to FIG.1, a CMTS 102, a cable modem 104, downstream communication 106 andupstream communication 108, are shown. CMTS 102 further includes a CMTSscheduler 102, a contention resolution algorithm 111 and connectionadmission control 112. Cable modem 104 includes a cable modem scheduler116 and a codec 117 (or activity detector). Each of these componentswill be briefly described next.

In general, cable modem 104 forwards or provides data via asynchronouscommunications on cable networks. Cable modem 104 receives data from auser that needs to be transferred via a cable network. For many types ofdata, in order for cable modem 104 to transfer the data via a cablenetwork it must request that CMTS 102 grant to it the necessarybandwidth. The scenario where cable modem 104 needs to request thenecessary bandwidth is described in detail in related U.S. patentapplication Ser. No. 09/783,404, filed Feb. 15, 2001.

Alternatively, when voice traffic is involved, CMTS 102 automaticallygrants bandwidth to cable modem 104. One reason for this automatic grantof bandwidth is that voice traffic (or traffic data) cannot toleratedelays in its transfer. Therefore, since constant voice traffic is sodeterministic (i.e., constant bit rate), the CMTS can generate bandwidthgrants at a certain periodicity without the need of bandwidth requestsfrom the data provider (e.g., cable modem). This service is referred toas unsolicited grant service in DOCSIS and is described below withreference to FIG. 2.

Packetized voice generates a fixed size packet at deterministicinstants. This means that cable modem 104 requires an upstreamtransmission opportunity at regular intervals of time. The periodicitydepends on packetization of voice. One example that is not meant tolimit the present invention is when G.711 PCM voice generates a byte ofdata every 125 microsecs or 64 Kbps. If these bytes are accumulated into10 ms packets, the packet size would be 80 bytes of data. Therefore,every 10 ms cable modem 104 will need enough upstream bandwidth totransmit 80 bytes of data.

The voice calls may be supported in a connection-based mode. The presentinvention will focus on voice traffic and ways of increasing theefficiency of providing bandwidth for voice traffic to a data providervia asynchronous communication mediums by suppressing silence. Ways ofincreasing the efficiency of providing bandwidth for voice traffic to adata provider via asynchronous communication mediums by suppressingsilence is described below in detail. First, a high level flowchart ofunsolicited grant service will be described next with reference to FIG.2.

In FIG. 2, control starts at step 202. In step 202, cable modem 104 senda connection request to CMTS 102 prior to starting a voice call. Aconnection connect consists of a grant interval and a grant size. Thegrant interval is the time period between successive grants. The grantsize specifies how big each grant needs to be. Control then passes tostep 204.

In step 204, CMTS 102 receives the grant interval and the grant size ofthe connection request. Control then passes to step 206.

In step 206, using the grant interval and the grant size of theconnection request, CMTS 102 (via connection admission control 112)either accepts or rejects the voice call. Control then passes to step208.

In step 208, if the call is accepted, then CMTS 102 generates bandwidthgrants for the service identifier as specified. The flowchart in FIG. 2ends at this point. Cable modem scheduler 116 is coupled to cable modem104 and codec 117. Cable modem scheduler 116 is described in detail inrelated U.S. patent application Ser. No. 09/783,404, filed Feb. 15,2001. In general, cable modem scheduler 116 is responsible formultiplexing the internal traffic. Codec 117 can detect silence periodsin upstream communication 108. Note that there is a bi-direction flowbetween codec 117 and cable modem scheduler 116 for the flow of data.There is a directional flow between codec 117 and cable modem scheduler116 for the flow of an early activity indicator. In an embodiment of thepresent invention, cable modem 104 signals for a reduction in itsbandwidth requirements at the beginning of silence periods and anincrease when the silence periods end. This will be described in moredetail in Section E below.

As stated above, DOCSIS is a common cable modem standard used today.DOCSIS provides standard centralized scheduling decisions that do notallow for flexibility in terms of deciding when or how cable modem 104requests bandwidth from CMTS 102 in order to transfer its current data.Cable modem scheduler 116 defines an architecture that overrules thisDOCSIS standard in a seamless manner. Some of the main differencesbetween the DOCSIS standard and cable modem scheduler 116 are describednext.

One main difference between the DOCSIS standard and cable modemscheduler 116 includes the decoupling of the request phase (for dataother than voice) with the grant phase (i.e., grants of bandwidthreceived from CMTS 102). For voice data, bandwidth grants are doneautomatically by CMTS 102 without cable modem 104 having to make anyrequests. Once bandwidth grants are received by cable modem 104, cablemodem scheduler 116 uses granted bandwidth as they are receivedregardless of their size and priority specification, thereby ignoringthe DOCSIS standard. Cable modem scheduler 116 ignores the priority idof the granted bandwidth. In addition, piggyback requests may beseparate requests for bandwidth instead of extended header as done inthe DOCSIS standard. How piggyback requests are handled by the presentinvention are described in detail in related U.S. patent applicationSer. No. 09/783,404, filed Feb. 15, 2001. Here, it is important to notethat piggybacks requests are treated as separate requests for bandwidthand may be given a priority identifier. In another embodiment,piggybacks requests are not assigned a priority identifier. CMTS 102,CMTS scheduler 110, connection admission control 112 and contentionresolution algorithm 111 will now be described.

CMTS 102 is a central device for connecting the cable network to a datanetwork. CMTS scheduler 102 is a bandwidth manager. CMTS scheduler 102,as a bandwidth manager that decides how to grant available bandwidthaccording to the current bandwidth requests. This grant for voicetraffic is done via downstream communication 106 in such as way as toreduce overhead by suppressing silence. This ability to decide how togrant available bandwidth provides flexibility. This flexibility allowsthe present invention to reduce the overhead involved in grantingbandwidth to cable modem 104 via downstream communication.

Contention resolution algorithm 111 decides how to use contentionminislots. Contention minislots are described in detail in related U.S.patent application Ser. No. 09/783,404, filed Feb. 15, 2001. Connectionadmission control 112 decides whether or not to admit more traffic inthe system. This is typically only used for voice traffic (e.g., step206 in FIG. 2 above).

As described above, the way in which the DOCSIS CMTS scheduler grantsbandwidth is quite restrictive, thus creating unnecessary overhead indownstream communication. The details of how CMTS scheduler 110 grantsbandwidth to cable modem 104 for voice traffic so that to decreaseoverhead by suppressing silence will be described in detail below. Next,the format of an individual voice packet is described with reference toFIG. 3.

C. Voice Header Format

FIG. 3 illustrates an example format of an individual voice packet usedby the present invention according to an embodiment. An individual voicepacket 310 includes a silence flag 304 (i.e., silence bit), a voicechannel identifier 306 (VIDO) and a voice payload 308. Silence flag 304and voice channel identifier 306 are attached to voice payload 308 tohelp in demultiplexing a byte. When silence flag 304 is set it indicatesthat the silence period starts. Voice packet 310 with the silence setcarries the silence flag parameters.

Also shown in FIG. 3 is a protocol data unit 302. Headers 303 ofprotocol data unit 302 are compressed to include silence flag 304 andvoice channel identifier 306 (VIDO) (i.e., the header of voice packet310).

In general, voice channel transmits the raw data without any headers.Requests can be piggybacked with voice transmissions, and they typicallyare included at the beginning of the raw voice data. Since CMTS 102grants the voice packet region, CMTS 102 knows the length of the voicepackets that are to be transmitted in this region. If the total messagelength is different it typically is due to the voice channels becomingsilent. The voice packets can be of different sizes if the voicechannels operate at different compression rates and packetizationintervals. However, the packet sizes are typically within a set of fixednumbers. Thus, CMTS 102 can demultiplex the piggybacking requestsincluded with the voice packet(s) without the need of additional packetdelimiters. The individual voice packets are typically demultiplexed ata higher protocol level. Next, the support of voice with activitydetection (AD) is described.

D. Support of Voice with Activity Detection (AD)

In general, in any conversation only one of the persons is speaking at agiven instant. Therefore, during a conversation only one half of thecircuit is needed at any given time. Typically, one side of theconversation is active for only 40% of the time. The present invention,by not transmitting any data during the silence periods and playing outbackground noise (i.e., comfort noise) through the user of noiseparameters at the other end, obtains significant bandwidth savings. Thistechnique of the present invention may be referred to as silencesuppression, or voice activity detection (VAD).

The effectively support this type of traffic depends, at least partly,on the need of transmission of noise parameters during the silenceperiods. The present invention incorporates at least two ways oftransmitting noise parameters during silence periods. The first wayinvolves assuming that the noise is completely regenerated at CMTS 102and hence cable modem 104 goes completely idle during the silence period(i.e., silence is eliminated). The second way involves transmitting thenoise parameters in a small packet. In this case, an activity detectionmechanism translates to a two state call with a fixed bandwidthrequirement during the active state, and a fixed, but smaller, bandwidthrequirement during the silence period. The present invention refers tothis as silence compression since the silence is compressed instead ofbeing eliminated.

In summary, traffic generated by a voice codec 117 can be of three typesin the present invention. These three types include: 1) constant voicegenerates constant rate for the duration of the call; 2) voice withsilence compression alternates two constant rates, high rate duringtalking periods and low rate during silent periods, and 3) voice withsilence suppression turns on a constant rate during talk periods andturns it off during silent periods. A form of the latter type, calledcontention-based silence suppression, will now be described.

E. Contention-Based Silence Suppression Overview

In general, a voice activity detection mechanism utilizes the fact thatone side of the conversation is active only 40% of the time. Codec 117can detect these silence periods in the upstream side of theconversation (or via upstream communication 108). Cable modem 104signals for a reduction in its bandwidth requirements at the beginningof silence periods and an increase when they end. Cable modem 104indicates silence to CMTS 102 via the bandwidth grant after a talkspurt. Call reactivation will be described next.

Silence suppression is supported by the present invention via callreactivation by using priorities in contention minislots. Alternatively,call reactivation is supported in DOCSIS using request polls. In DOCSIS,during silence periods, the unsolicited grants are stopped and requestpolls are sent instead. These polls are defined to send the reactivationrequest when the call goes active again. However, a voice call is silentin the order of a few seconds. It is obvious that any kind of pollingresults in a large amount of overhead. A way to reduce this overhead isaccomplished by the present invention via its call reactivationmechanism by using priorities in contention minislots. Here, overhead isreduced by 1) eliminating the polls, 2) letting them share across allvoice calls, and 3) less contention minislots are needed to transmitsuccessfully a request as compared to the continuous polls. FIG. 4 is aflowchart illustrating the steps involved in reactivation mechanism ofusing priorities in contention minislots according to an embodiment ofthe present invention.

In FIG. 4, control starts at step 402. In step 402, cable modemscheduler 116 assigns the highest priority level to all voice streams.Control then passes to step 404.

In step 404, CMTS scheduler 110 periodically allocates contentionminislots to the highest priority level. Control then passes to step406.

In step 406, a successful contention request is an indication for CMTSscheduler 110 to restart sending unsolicited bandwidth grants. Controlthen passes to step 408.

In step 408, CMTS scheduler 110 updates the amount of contentionminislots to allocate for voice service so that the reactivation timedoes not affect the quality of the voice conversation. This step isfurther described below in Section G. The flowchart in FIG. 4 ends atthis point. Next, the activation and deactivation of unsolicited grantservice is described in the following section.

F. Activation/Deactivation of Unsolicited Grant Service inContention-Based Silence Suppression

The deactivation of unsolicited grant service (i.e., deactivating a callwhen the call goes silent) will be described first with reference toFIG. 5. Then the activation of unsolicited grant service (i.e.,activating a call when the call becomes active) will be described withreference to FIG. 6.

FIG. 5 starts at step 502. In step 502, codec 117 determines that thecall has become silent in upstream communication 108. Control thenpasses to step 504.

In step 504, cable modem scheduler 116 sends a single byte of data toCMTS 102 in the current unsolicited grant service with the silence flagset (i.e. set silence flag 304 in voice packet 310 from FIG. 3). The setsilence flag is sent whenever it happens. Note, that the single byte ofdata to CMTS 102 can also be done in the last packet. Control thenpasses to step 506.

In step 506, CMTS scheduler 110 stops the unsolicited grant service onreceiving protocol data unit 302 with silence flag 304 set. Theflowchart in FIG. 5 ends at this point.

The activation of unsolicited grant service (i.e., activating a callwhen the call becomes active) will now be discussed. In general, anadditional bandwidth request from cable modem scheduler 116 isconsidered as a request to reactivate the call. This reactivationmessage can be sent either in a contention minislot or piggybacked in agranted region, as described next in FIG. 6. Note that codec 117 can beused by the present invention to provide an early indication toreactivate the grant service faster.

FIG. 6 starts at step 602. In step 602, cable modem scheduler 116 waitsfor a period of time for CMTS 102 to schedule an unsolicited bandwidthgrant via downstream communication 106. Control then passes to step 604.

In step 604, if the grant arrived within the period of time, thencontrol passes to step 606. Alternatively, control passes to step 608.

In step 606, cable modem scheduler 116 piggybacks the reactivationrequest in the grant to be sent to CMTS 102 via upstream communication.The flowchart in FIG. 6 ends at this point.

In step 608, cable modem scheduler 116 sends the reactivation message ina priority contention minislot. The flowchart in FIG. 6 ends at thispoint.

There are three alternative reactivate request methods that the presentinvention may utilize. The first is referred to as an ASAP policy. Here,cable modem scheduler 116 sends the reactivate request in the firstavailable opportunity (either in the first voice contention minislot orin the first grant). The second alternative reactivate request method isreferred to as a maximize piggyback method. Here, cable modem scheduler116 waits for a grant if there is another call that is active. The thirdalternative reactivate request method deals with waiting for a grant tosend the reactivation message if a grant that is will meet latencyconstraints is guaranteed to arrive. Otherwise, send the reactivaterequest in the first voice contention minislot. In any case, if a grantcomes before knowing the result of the contention request, cable modemscheduler 116 will send the reactivation again. The duplicatedactivation will be discarded by CMTS 102.

The present invention also can deal with inactive calls in an efficientmanner. Here, the present invention implements an inactivity timer. Ifthe number of unused unsolicited grants is above a threshold, then stopthe unsolicited grants and start give it a poll. The determination ofthe number of voice contention minislots to be generated incontention-based silence suppression (step 410 in FIG. 4) will bedescribed next in Section G.

G. The Determination of the Number of Voice Contention Minislots To BeGenerated in Contention-Based Silence Suppression

In general, the number of voice contention minislots to be generateddepends on the number of active voice streams according to an embodimentof the present invention. Typically, the most conservative case is toconsider the worst case which corresponds to having the maximum numberof voice streams that the particular system can support.

An algorithm or method used by the present invention to determine thenumber of contention minislots needed for voice priority requires thefollowing defined notation:

-   -   T=periodicity of contention minislots in seconds;    -   λ=mean silence duration in seconds;    -   N=number of calls in silent state; and    -   Pc=probability of collision having N number of calls in silent        state.

The periodicity in seconds of contention minislots can be computed byusing the formula shown in FIG. 7. An example utilizing the formula inFIG. 7 will be described. This example is for illustration purposes onlyand does not limit the present invention. If the mean silence duration(λ) is 2.35 s and there are 50 calls silent (N) at a given instant andit is desired to restrict the probability of collision (Pc) to 10ˆ−3,then the spacing that needs to be chosen between priority contentionslots is 1.5 ms (=−2.35* log (1−10ˆ−1.5/49). But, one collision in athousand attempts is overprovision of bandwidth.

Initial simulations have shown that with 1 voice priority contentionslot per 100 upstream slots (1% overhead) the delay in activating theunsolicited grant service may be less than 5 ms. Based on these results,the present invention specifies that CMTS scheduler 110 should allocateone contention minislot for voice priority for every 200 minislots onthe upstream. The relationship between the periodicity of contentionminislots (T) and the probability of collision (Pc) for several numbersof silent users (N) is shown in FIG. 8. Early indication for callreactivation in contention-based silence suppression is described nextin Section H.

FIG. 10 is a flowchart that illustrates how the present inventiondetermines the number of contention minislots needed for voice priority.FIG. 10 starts in step 1002. In step 1002, the number of calls in silentstate is determined. Control then passes to step 1004.

In step 1004, the number of contention minislots required is calculatedto restrict the probability of collusion to a specific value. Controlthen passes to step 1006.

In step 1006, indicate the calculated number of contention minislots toCMTS scheduler 110. Control then passes to step 1008.

In step 1008, CMTS scheduler 110 allocates the calculated number ofcontention minislots for the voice priority. Control then passes to step1010.

In step 1010, cable modem 104 uses the voice priority contentionminislots to send a bandwidth request to reactivate the call. Theflowchart in FIG. 10 ends at this point.

H. Early Indication for Call Reactivation/Deactivation inContention-Based Silence Suppression

The packetization of voice helps the present invention to indicate toCMTS 102 (i.e., in the MAC layer) earlier, the need to reactivate theunsolicited grant service. This is due to the fact that the voice packetis generated once every packetization interval. The call is equallylikely to become active anytime during that interval. If the presentinvention allows a voice activity detector to indicate to the MAC layeras soon as the call is active, then the MAC layer can start the processof reactivating the unsolicited grant service stream half apacketization interval earlier. This early indication helps to reducethe jitter in reactivating the voice call when it transitions fromactive to silent. The same indication helps for early indication forcall deactivation by indicating the silence in the last packet.

I. Example Environment of the Present Invention

CMTS 102, CMTS scheduler 110, cable modem scheduler 116, connectionadmission control 112, codec 117 and contention resolution algorithm 111may be implemented using computer 900 as shown in FIG. 9. Obviously,more than one of these finctional components could be implemented on asingle computer 900.

The present invention may be implemented using hardware, software or acombination thereof and may be implemented in a computer system or otherprocessing system. In fact, in one embodiment, the invention is directedtoward one or more computer systems capable of carrying out thefunctionality described herein. The computer system 900 includes one ormore processors, such as processor 904. The processor 904 is connectedto a communication bus 906. Various software embodiments are describedin terms of this example computer system. After reading thisdescription, it will become apparent to a person skilled in the relevantart how to implement the invention using other computer systems and/orcomputer architectures.

Computer system 900 also includes a main memory 908, preferably randomaccess memory (RAM), and can also include a secondary memory 910. Thesecondary memory 910 can include, for example, a hard disk drive 912and/or a removable storage drive 914, representing a floppy disk drive,a magnetic tape drive, an optical disk drive, etc. The removable storagedrive 914 reads from and/or writes to a removable storage unit 918 in awell known manner. Removable storage unit 918, represents a floppy disk,magnetic tape, optical disk, etc. which is read by and written to byremovable storage drive 914. As will be appreciated, the removablestorage unit 918 includes a computer usable storage medium having storedtherein computer software and/or data.

In alternative embodiments, secondary memory 910 may include othersimilar means for allowing computer programs or other instructions to beloaded into computer system 900. Such means can include, for example, aremovable storage unit 922 and an interface 920. Examples of such caninclude a program cartridge and cartridge interface (such as that foundin video game devices), a removable memory chip (such as an EPROM, orPROM) and associated socket, and other removable storage units 922 andinterfaces 920 which allow software and data to be transferred from theremovable storage unit 918 to computer system 900.

Computer system 900 can also include a communications interface 924.Communications interface 924 allows software and data to be transferredbetween computer system 900 and external devices. Examples ofcommunications interface 924 can include a modem, a network interface(such as an Ethernet card), a communications port, a PCMCIA slot andcard, etc. Software and data transferred via communications interface924 are in the form of signals which can be electronic, electromagnetic,optical or other signals capable of being received by communicationsinterface 924. These signals 926 are provided to communicationsinterface via a channel 928. This channel 928 carries signals 926 andcan be implemented using wire or cable, fiber optics, a phone line, acellular phone link, an RF link and other communications channels.

In this document, the terms “computer program medium” and “computerusable medium” are used to generally refer to media such as removablestorage device 918, a hard disk installed in hard disk drive 912, andsignals 926. These computer program products are means for providingsoftware to computer system 900.

Computer programs (also called computer control logic) are stored inmain memory and/or secondary memory 910. Computer programs can also bereceived via communications interface 924. Such computer programs, whenexecuted, enable the computer system 900 to perform the features of thepresent invention as discussed herein. In particular, the computerprograms, when executed, enable the processor 904 to perform thefeatures of the present invention. Accordingly, such computer programsrepresent controllers of the computer system 900.

In an embodiment where the invention is implemented using software, thesoftware may be stored in a computer program product and loaded intocomputer system 900 using removable storage drive 914, hard drive 912 orcommunications interface 924. The control logic (software), whenexecuted by the processor 904, causes the processor 904 to perform thefinctions of the invention as described herein.

In another embodiment, the invention is implemented primarily inhardware using, for example, hardware components such as applicationspecific integrated circuits (ASICs). Implementation of the hardwarestate machine so as to perform the functions described herein will beapparent to persons skilled in the relevant art(s). In yet anotherembodiment, the invention is implemented using a combination of bothhardware and software.

CONCLUSION

While various embodiments of the present invention have been describedabove, it should be understood that they have been presented by way ofexample, and not limitation. It will be apparent to persons skilled inthe relevant art that various changes in form and detail may be madetherein without departing from the spirit and scope of the invention.This is especially true in light of technology and terms within therelevant art(s) that may be later developed. Thus, the present inventionshould not be limited by any of the above-described exemplaryembodiments, but should be defined only in accordance with the followingclaims and their equivalents.

1. A method for suppressing silence in bidirectional communicationsbetween a centralized node and a plurality of local nodes in anasynchronous network environment, comprising the steps of: detecting asilent period in an upstream channel, said upstream channel transmittingdata from a local node; and deactivating unsolicited grant service andnot activating request polling in response to said detecting a silentperiod.